More thoughts on 3e and then an explanation of why I actually am running a Pathfinder game.
Combat - Takes forever. In some ways I love playing on a battlemat, in some ways I don't. I like the visual representation (although a white board works just fine if you need something to track things on) - especially for complex combats, but this is where all the rules monkeying tends to crop up.
I had a player (in a different game than the one I am running now) once try to leap through the air and punch a flying griffin that was about 10 feet up and 20 feet away. I said "no way" and this devolved into a big discussion of the jumping rules and the player saying my favorite line: "but this is what my character does."
I thought that all of this rules minutiae was defended on the grounds of realism?
The same goes for movement and attacks of opportunity, so yes, it is realistic that someone will try to strike you if you try to pass by or cast a spell, but they won't take one step to do so? Not realistic, (not that I care), but let's not try to pretend that these rules are based on anything closer to reality than AD&D was.
Rule completeness - Its a myth. No rule set is entirely complete or coherent. Example from last session:
Group of 3rd level characters (we picked up where a campaign I ran last summer left off) has been exploring the dungeon and generally kicking ass in true 3e manner. There is no rogue so the barbarian is hacking through doors. Each time he does this I take the opportunity to roll for a random encounter). Finally one hits and . . . swarm of bats! Well this a melee heavy group so they all say "uh oh, swarm". They have exactly one AoE spell among the five of them. Burning hands goes off . . . and doesn't kill them. So the witch cleverly pulls out a vial of acid and throws it amidst the swarming bats. Well, apparently grenade-like weapons use the touch AC of the opponent. Bats have a very high touch AC. It is very tough to touch a bat. Of course that isn't what he is doing. He is not trying to touch one and cast shocking grasp. He is merely trying to throw a glass vial onto the floor and have it splash on them. So he misses. This is a ridiculous result to the action he is attempting to take. So . . . house rule, he hits automatically! Unfortunately this doesn't kill the bats either and they have to flee . . . but at least things are making sense now.
So don't claim that the rules cover everything or always coherent. Just as much a need for adjudication as ever, just now we have to look a lot of things up first.
So why DO I play Pathfinder?
Because I have found a good group of players who like to play it and I like DMing. They know the rules well and are good sports so I don't need to memorize things. Generally they tell me the rules, we look it up if it is very important or there is disagreement, and I adjudicate. I don't mind DMing (sorry WotC, GMing) Pathfinder because I like designing adventures, dungeons, and monsters. The rules system is pretty irrelevant to all of that.
Would I rather play a different rules system? Sure. Would I be a better DM if we played something I was more familiar with? Probably. But I think that with a good group rules adjudication is the smallest part of the DM's job. Will they start seeing monsters from the Swords & Wizardry Monster Book that arrived last night? Absolutely.
Basically, rule systems are pretty irrelevant to the kind of stories we tell. That's just the details. That's why I think simple rules are good, but if my players would rather get all bogged down in that stuff I'm okay with that. They just need to understand that I think CR is a laughable concept, and that yes I am going to kill them with the cave giant waiting by the stairs.